Fix supporting <link> in markdown as it is supposed to be
    
    Fixes https://pagure.io/pagure/issue/2906
    
    This currently doesn't work well for <irc: ...=""> links, supposedly due</irc:>
    to something in the regex but not sure what it is.
    
    Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr></pingou@pingoured.fr>